Conductive bottom filler material and method of making the same



Patented Dec. 22, 1942 CONDUCTIVE BOTTOM FILLER MATERIAL AND METHOD OFMAKING THE SAME Anthony Siers, Humboldt, Tenn, assignor to ODonnell ShoeCompany, Humboldt, Tenn., a corporation of Minnesota No Drawing.Application July 7, 1941, Serial No. 401,399

3 Claims. (Cl. 260-750) The present invention relates to an improvedconductive bottom filler material for electrically conductive shoes andto a method whereby the ingredients which cooperate to makeup suchfiller material are rendered conductive.

More specifically, the invention relates to a method of treating groundcork, leather scraps, asbestos fiber, sawdust and other base materialand combining them with a suitable binder material in such a manner asto produce a conductive filler material which is adapted for use infilling in the space existing between the inturned margins of the upperand the inner and outer soles of conductive shoes of the type havingconductive outer and inner soles.

Filler material manufactured in accordance with the principles of thepresent invention, although distinguished from ordinary materials ofthis nature by possessing a definite degree of conductivity, retains toa marked degree all of the beneficial characteristics of a high gradebottom filler material and is capable of being prepared as an article ofmanufacture and packaged in bulk in a self-sustaining form capable ofbeing kept indefinitely for such period as required before being usedand thereafter molded into a shoe bottom at room temperatures toconstitute a tenacious layer meeting all shoemakers requirements.

The principal object of the present invention is to provide an improvedfiller composition for shoes, together with a method of preparing thesame which will not only meet the ordinary conditions required for itsready application to the cavities of shoe bottoms and during thesubsequent steps of constructing the shoe, fill the cavity between theinner and outer soles and adhere firmly to the walls of the shoe cavity,impart to the bottom of the finished shoe the permanent flexibilitydesired without shifting and losing its form and without drying out andbecoming brittle with age, but which also will afford a conductive pathfor static discharges through the shoe from the conductive inner sole tothe conductive outsole and from thence to the ground.

A further object of the invention is to provide such a filler materialwhich, although characteristically conductive, is characterized by anabsence of metallic particles and which may be used in the shoe for thepurpose of establishing electrical contact between the inner and outersoles without necessitating the utilization of metallic inserts and thelike.

Yet another object of the invention is to pro- 55 vide a bottom fillermaterial for shoes, which. will retain its conductive propertiespermanently and which properties remain substantially constant and arenot affected either by age, temperature or humidity of the surroundingatmosphere. In other words, according to the present invention, theimproved conductive filler material retains its required degree ofconductivity even when conditions of humidity are at an absoluteminimum, i. e., when the humidity drops to zero.

Other objects and advantages of the invention will appear from thefollowing description.

According to the present invention a degree of conductivity is impartedto the materials going in to make up the bottom filler material baseand, after the required degree of conductivity is attained, the basematerials are intimately mixed with a conductive binder material, theconductivity of the mixture depending upon and being a factor of theseparate conductivities of the binder and the base.

Among the base materials that are found practicable are ground cork,leather scrap, asbestos fiber, and sawdust, all of which in theiroriginal state are substantially non-conductive when dry. For the bindermaterial, I prefer to utilize commercial conductive rubber cement. Oneform of such a conductive rubber cement is known to the trade as SpecialCarbon P-33 and consists of rubber which is loaded with approximatelypure carbon black.

In the treatment of dry cork or other base materials, the pulverizedcork or other material is submerged in a solution obtained by dissolvingone and one-half pounds of lithium chloride, onehalf pound of calciumchloride and one-half pound of sodium chloride, in suiiicient water tomake up a total solution content of one gallon. The solution may beheated, if desired, but little benefit is obtained thereby andconsequently, it is preferred that the submersion of the pulverized corkor other material be performed at room temperatures. The materials areallowed to remain in the solution for a period of time not less than sixhours and preferably ten hours and thereafter, they are removed anddrained and thereafter allowed to partially dry. If desired, the processmay be hastened by employing forced drying with or without the use ofheat. Where the time factor is not important, no heat or forced dryingis resorted to and the ultimate conductivity of the materials is notaltered.

After the above treatment of the base material the partially dry cork orother material is thoroughly mixed with commercial conductive cementcontaining carbon black and to which there has been added a benzolsolution of rosin in the proper amount to obtain the required degree ofadhesiveness. While according to the present method, rosin is thepreferred substance for this purpose, other substances, such as resinobtained from gum, rosin oil, tar, asphalt, dextrin, etc, may be used.

While the specific proportions of the ingredients may be varied,suitable filler material may be obtained by mixing at least six ouncesof liquefied wood rosin in the smallest amount of benzol which willassimilate it, thus obtaining a. practically saturated solution of resinin benzol. A suitable consistency may be obtained by dissolving sixounces of the rosin in from one pint to one quart of the benzol.

The mixture is gradually stirred at room temperatures into one gallon ofthe conductive rubber cement which may be the aforesaid Special CarbonP-33 and after thorough mixture of these materials, a suitable amount ofthe previously treated ground cork or other base material is added orstirred into the solution. For each gallon of the solution from two tothree pounds of the base material is employed. The adhesiveness of theultimate product may be varied by varying the amount of rosin employed.The less rosin contained in the product, the less will be the degree ofadhesiveness. The adhesiveness may also be varied by varying thematerials em ployed as for example, utilizing in place of the benzolother substances such as tar, asphalt or the like.

The materials when treated and mixed as above described are thus broughtto their final condition and afford an extremely efficient conductivefiller material well adapted to perform the functions required of itwhen utilized in a shoe assembly. The material is freely plastic whenapplied in a cold condition at room temperatures and makes intimatecontact with and adheres uniformly to the walls of the shoe cavity.

After the outer sole has been attached to the shoe and the shoe isfinished the composition does not readily deform or shift its position,either spontaneously or under the usual temperatures and pressures towhich it is exposed under the weight of the foot. The material retainsits conductive properties indefinitely regardless of conditions oftemperature and humidity and the extent of this conductivity is in theneighborhood of 100,000 ohms when measured between two test prods placedon opposite sides of a cubic inch molded block of the material.

Finally, the finished product is found to have no appreciable odor overand above the nondisagreeable odor of the rubber cement material and thecolor thereof is a grayish or brownish black, depending upon the amountand character of the filler material or base.

The invention is not to be limited to the exact method herein set forthor to the specific materials or solutions employed in carrying out themethod as various changes in the method and in the ingredients employedare contemplated.

What is claimed is:

1. The method of preparing a bottom filler material for shoes whichconsists in submerging at room temperatures dry ground cork in asolution of the chlorides of sodium, calcium and lithium and thereaftermixing at room temperatures the cork material with conductive rubbercement containing carbon block and to which there has been added aquantity of benzol.

2. The method of preparing a bottom filler material for shoes, whichconsists in submerging at room temperatures approximately two andone-half pounds of dry cork in a solution consisting of approximatelyone and one-half pounds of lithium chloride, one-half pound of calciumchloride and one-half pound of sodium chloride dissolved in sufficientwater to make up one gallon of solution, partially drying the materialwhich has previously been submerged, and thereafter mixing the quantityof thus treated cork intimately with approximately one gallon ofconductive rubber cement consisting of approximately equal amounts ofrubber and pure carbon black to which cement there has been addedapproximately one quart of a saturated solution of rosin in benzol.

3. The method of preparing a bottom filler material for shoes whichconsists in submerging dry ground cork in a solution of the chlorides ofsodium, calcium and lithium, withdrawing the cork and allowing the sameto partially dry, and thereafter mixing at room temperatures thepartially dry treated cork material with conductive rubber cementconsisting of approximately equal amounts of rubber and pure carbonblack to which there has been added a quantity of benzol.

ANTHONY SIERS.

